Weird Linker Error - c++

Question

#include path
include_directories(
${PROJECT_SOURCE_DIR}/include
${HGE_INCLUDE_DIR}
${IKL_INCLUDE_DIR}
${BOOST_DIRECTORY}
)
#include all files
FILE(GLOB CORE_SRCS source/core/*.cpp)
FILE(GLOB TOOL_SRCS source/tools/*.cpp)
FILE(GLOB GAME_SRCS source/game/*.cpp)
#Making a compiled library
add_library(GAMECORE_LIBRARY ${CORE_SRCS} ${HGE_LIBRARY} ${HGE_HELPER_LIBRARY})
#add executable
add_executable(DemoGame ${GAME_SRCS})
##link executable to HGE lib
TARGET_LINK_LIBRARIES(DemoGame ${HGE_LIBRARY} ${HGE_HELPER_LIBRARY} ${IKL_LIBRARY} GAMECORE_LIBRARY)
if(BUILD_TOOLS)
add_executable(EntityTool ${TOOL_SRCS})
TARGET_LINK_LIBRARIES(EntityTool ${HGE_LIBRARY} ${HGE_HELPER_LIBRARY} ${IKL_LIBRARY} GAMECORE_LIBRARY)
endif(BUILD_TOOLS)
this is my current cmake ..
I get a weird linker error for hgeGUI class
eg : DemoGame/source/core/GameMainMenu.cpp:74: undefined reference to `hgeGUI::hgeGUI()'
This only happens when I try to compile the core files into a static library.
When I add the executable with the CORE_SRCS and remove the dependencies on my current compiled library .. it will work fine..
Also I tried copy pasting the hgegui.cpp file into my core sources directory .. and change the #include "..\..\include\hgegui.h" to #include "hgegui.h"
After that my linker code resolves the issue but I get segmentation faults but I m guessing linking the file in the previous step was not right ..
Here's a link to their .h file
http://trac.assembla.com/snowscape/browser/hge/include/hgegui.h

Answer 1

It looks like you're misusing the ${HGE_LIBRARY} and ${HGE_HELPER_LIBRARY} variables.
In an add_library call, you include all the source files which make up that library.
In a target_link_libraries call, you specify libraries or flags to use when linking the target.
So, if ${HGE_LIBRARY} and ${HGE_HELPER_LIBRARY} specify paths to libraries which you want to specify as dependencies of GAMECORE_LIBRARY, you need to do:
add_library(GAMECORE_LIBRARY ${CORE_SRCS})
target_link_libraries(GAMECORE_LIBRARY ${HGE_LIBRARY} ${HGE_HELPER_LIBRARY})
The dependencies are transitive, so this means when you specify GAMECORE_LIBRARY as a dependency of DemoGame and EntityTool, then CMake recognises that ${HGE_LIBRARY} and ${HGE_HELPER_LIBRARY} are also dependencies, so you can remove them from the target_link_libraries calls for DemoGame and EntityTool if you want.
For further info on add_library and target_link_libraries, run:
cmake --help-command add_library
cmake --help-command target_link_libraries